U.S. Pat. No. 3,565,292 discloses a fluid feeding device in which a movable piston is biased directly by a compression spring to move away from a stationary plate and compress a fluid bag for feeding fluid therefrom, and a screw extending vertically from the piston through the stationary plate has a handle threaded on the screw and bearing against the exterior of the stationary plate. Rotating the handle in one direction moves the piston toward the stationary plate and compresses the spring, and rotating the handle in the opposite direction allows the piston to move away from the stationary plate by spring action to compress the bag. A disadvantage of this device is that as the bag is compressed the spring pressure decreases and varies the rate of fluid flow, and it is very important in feeding blood to a patient, for example, to maintain the fluid flow substantially constant.